You could check also if running Firestrike (benchmark for systems, not made with UE) the same issue happens, that would at least give a hint if your power supply is to blame. I have used the following tool to check your system specs against and setting the max speed and voltage to processor (4.7GHz and 1.45V) it is still safe for a 650W PSU (it asks for a 615W as recommended). It is necessary to supply the correct values for the graphics card regarding the speed.
http://www.coolermaster.com/power-supply-calculator/
A tech had me run extreme benchmark testing using both furmark and p95 at the same time. PC passed with flying colors and temps were great. It also passes heaven benchmark.